1. Field of the Invention
The present invention relates to a disc recording and/or reproducing apparatus (will be referred to as xe2x80x9cdisc drivexe2x80x9d hereinunder) for recording and/or reproducing data to and/or from a disc-shaped recording medium such as an optical disc, magnetic disc, etc., and more particularly to a disc drive including a servo signal writing apparatus to write servo signals to a disc-shaped recording medium.
Also, the present invention relates to a servo signal writing apparatus used to write servo signals to a disc-shaped recording medium such as an optical disc, magnetic disc, etc.
2. Description of Related Art
Since tracking is controlled during write or read of data to or from a disc in a conventional disc drive such as a hard disc drive, the disc as a recording medium should have previously formed thereon tracks each defining a radial writing position.
Thus, in a disc drive before shipment from the factory, a magnetic head incorporated in the disc drive is used to write tracking servo signals to a disc used in the disc drive to form such tracks on the disc.
However, such a disc drive cannot control the position of the magnetic head if no servo signals are recorded on the disc. To write servo signals to a disc having no signal recorded thereon, a servo signal writing apparatus is used which controls the disc-radial position, etc. of the magnetic head to write servo signals to the disc.
Various servo signal writing apparatus have so far been proposed, of which a typical one is well known which has an encoder installed to a magnetic head holding arm to control the position of the magnetic head to record servo signals to the magnetic disc. In this servo signal writing apparatus, the encoder is installed with a fixing pin to the magnetic head holding arm, and the moving position of the magnetic head is controlled to record the servo signal. Since in this servo signal writing apparatus, the magnetic head holding arm is mechanically connected, however, there will take place a difference in installed condition of the magnetic head holding arm between when the servo signal is recorded on the disc and when the servo signal is used in practice, so that the servo signal can hardly be recorded with an improved accuracy. Also, since the closed disc drive has to be opened for the actual use of the servo signal, the servo signals must be written to the disc in a clean room, which will lead to an increase of manufacturing costs.
Further, in another example of the servo signal writing apparatus, a servo loop is formed for a pit or groove formed in the magnetic head holding arm to follow a laser light emitted from an optical head, and a servo loop is formed to detect, by an encoder, a moving position of the optical head emitting the laser light to control the moving position of the optical head, thereby controlling the moving position of the magnetic head to write servo signals to a disc. Since this apparatus controls the moving position of the magnetic head by the use of the laser light emitted from outside the disc drive, the servo signal can be written with no contact with the magnetic head holding arm. Therefore, different from the above-mentioned apparatus, this apparatus makes it unnecessary to write servo signals to a disc in the clean room or the like. In this servo signal writing apparatus, however, it is necessary to form the two servo loops, one for allowing the magnetic head holding arm to follow the movement of the optical head and the other for controlling the position of the optical head based on a detection output from the encoder. Thus the apparatus can hardly write servo signals with an improved accuracy and at a high speed.
To solve the above-mentioned problems involved in the conventional servo signal writing apparatuses, the Inventor of the present invention had proposed servo signal writing apparatuses as disclosed in the Provisional Publication of the Japanese Patent Application Nos. 4-351766 and 4-351767, respectively. In a hard disc drive comprising a scale provided on a magnetic head holding arm and which has a diffraction grating formed thereon, the servo signal writing apparatus detects the diffraction grating on the scale to write servo signals to the hard disc.
Referring now to FIG. 1, there is illustrated the servo signal writing apparatus proposed by the Inventor of the present invention.
In FIG. 1, the servo signal writing apparatus is generally indicated with a reference 100, and a hard disc drive in which servo signals are written to a disc is generally indicated with a reference 110. The hard disc drive 110 comprises an enclosure 111, and a magnetic disc 112, magnetic head 113, arm 114 and an arm support 115 provided inside the enclosure 111.
As will be seen in FIG. 1, the arm 114 has the magnetic head 113 provided at one end thereof. The arm 114 is installed at the other end thereof to the arm support 115. The arm support 115 has built therein a voice coil motor which will drive the arm 114 when it is supplied with a drive current. As the arm 114 is driven by the voice coil motor provided inside the arm support 115, the arm 114 will be turned about a pivot 114a provided at one end portion thereof in a plane parallel to a signal recording surface of the magnetic disc 112. As the arm 114 turns in this way, the magnetic head 113 will move from the lead-in area toward the lead-out area, for example, of the magnetic disc 112. Thus, the magnetic head 113 is movable radially of the magnetic disc 112 to write data on the entire recording area of the magnetic disc 112. The rotating angle of the arm 114 varies depending upon the length of the arm 114 and size of the magnetic disc 112. The angle of rotation is about 30xc2x0, for example.
In the hard disc drive 110, the arm 114 has a scale 116 installed thereon near the base end thereof. As the arm 114 turns, the scale 116 is turned along with the magnetic head 113 in a plane parallel to the magnetic disc 112. The scale 116 has formed thereon a diffraction grating indicating a disc-radial position of the magnetic head 113. The diffraction grating formed on the scale 116 can be read by irradiating a laser light onto the diffraction grating from outside the hard disc drive 110. For example, a portion of the enclosure 111 opposite to the scale 116 is formed from a transparent material such as acryl, glass or the like so that the diffraction grating can be read from outside.
The diffraction grating formed on the scale 116 is recorded over a width L as shown in FIG. 2. The recorded width L is larger than the movable range of a portion of the arm 114 where the scale 116 is provided, so that the diffraction grating can be detected even when the magnetic head 113 has moved from the lead-in area to the lead-out area on the magnetic disc 112 (for example, when the arm 114 turns through an angle of about 30xc2x0).
As shown in FIG. 1, the conventional servo signal writing apparatus 100 to write servo signals to the disc in the hard disc drive 110 constructed as in the above, comprises an optical head 101 to irradiate a laser light onto the scale 116 and detect a reflected laser light from the scale 116, thereby detecting the diffraction grating formed on the scale 116, and a control circuit 102 to receive a detection signal from the optical head 101 and produce a magnetic head drive signal and servo signal for use to drive the magnetic head 113 based on the received detection signal.
The optical head 101 irradiates a laser light to the diffraction grating formed on the scale 116. The diffraction grating diffracts the incident laser light. The optical head 101 detects the reflected laser light diffracted by the diffraction grating to detect a phase component of the reflected laser light. As the arm 114 turns, the scale 116 provided thereon also turns along with the arm 114. The phase of the reflected laser light from the diffraction grating varies as the arm 114 turns. Thus, by detecting the phase component, it is possible to detect a disc-radial moving position of the magnetic head 113. The optical head 101 provides the control circuit 102 with the phase component of the reflected laser light as a position signal indicative of the moving position of the magnetic head 113.
Based on the position signal supplied from the optical head 101, the control circuit 102 provides a servo control of the magnetic head 113 to move the latter to a predetermined track position on the magnetic disc 112, and also drives the magnetic head 113 to write the servo signal to the predetermined track position on the magnetic disc 112.
In the hard disc drive 110, the recorded width L of the diffraction grating on the scale 116 is larger than the movable range of a portion of the arm 114 where the scale 116 is provided, as shown in FIG. 2.
Thus, the servo signal writing apparatus 100 can detect the diffraction grating even when the magnetic head 113 has moved from the lead-in area to the lead-out area on the magnetic disc 112. Hence, the magnetic head 113 can be moved over the signal recording area on the magnetic disc 112 to write a servo signal to each of all tracks on the magnetic disc 112.
Since the servo signal writing apparatus 100 proposed by the Invention of the present invention can write servo signals to a magnetic disc without any contact with the hard disc drive 110 as mentioned above, it is not necessary to write servo signals in a clean room. And since two servo loops may not be formed, servo signals can be written with an improved accuracy and at a high speed.
Recently, along with disc recording and/or reproducing apparatuses of larger capacities having been proposed, magnetic discs having a narrower track width have been proposed to cope with the larger capacity of the disc recording and/or reproducing apparatuses. Thus, a servo signal writing apparatus is required which can write servo signals to a magnetic disc with a higher density.
To write servo signals with a higher density by the servo signal writing apparatus 100 proposed by the Inventor of the present invention, the wavelength of the diffraction grating formed on the scale 116 may be shortened to control the position of the magnetic head 113 with a higher resolution, for example. In this case, however, the shorter wavelength of the diffraction scale will result in a larger cost for manufacturing the scale 116.
Further, to write servo signals with a higher density by the servo signal writing apparatus 100 proposed by the Inventor of the present invention without changing the wavelength, etc. of the diffraction grating formed on the scale 116, the scale 116 may be provided on the magnetic head holding arm 114 at a position nearer to the free end of the arm 114, that is, nearer to the magnetic head 113, for example. By locating the scale 116 at a position farther from the pivot 114a of the arm 114, the scale 116 can be turned through a larger angle than the angle through which the arm 114 is turned with the scale 116 disposed nearer to the pivot 114 as previously mentioned. In this case, however, the scale 116 has to be large enough for the diffraction grating formed thereon to be detected even when the magnetic head 113 has been moved from the lead-in area to the lead-out area on the magnetic disc 112 (for example, when the arm 114 is turned through an angle of about 30xc2x0).
However, if a large scale 116 is installed on the arm 114, it will add to the total mass of the arm 114. Thus, a large current has to be supplied to the voice coil motor to drive the arm 114, which will increase the power consumption. The increase in mass of the arm 114 will cause the mechanical frequency characteristic to be worse, so that the arm 114 cannot easily be positioned and the time required for data input to the hard disc drive 110 is increased.
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing a disc recording and/or reproducing apparatus adapted to implement a high accuracy, high resolution and a low cost in writing servo signals.
Also the present invention has another object to provide a servo signal writing apparatus adapted to implement a high accuracy, high resolution and low cost in writing servo signals.
The above object can be attained by providing a disc recording and/or reproducing apparatus comprising:
a read/write head to write and/or read a signal to and/or from a disc;
means for holding and moving the read/write head radially of the disc; and
a scale adapted to be movable, along with the read/write head provided on the read/write head holding means, radially of the disc and having recorded thereon a position information indicative of a moving position of the read/write head and which is readable from outside;
the position information recorded on the scale indicating a smaller range than the radial length of a signal recording area on the disc.
The disc recording and/or reproducing apparatus writes servo signals to a disc provided therein by controlling, by means of an external apparatus, the disc-radial position of the read/write head based on the position information indicative of the smaller range, recorded on the scale, than the radial length of the signal recording area on the disc.
The above object can be attained also by providing a servo signal writing apparatus for writing servo signals to a disc provided in a disc recording and/or reproducing apparatus comprising a read/write head to write and/or read a signal to and/or from a disc; means for holding and moving the read/write head radially of the disc; and a scale adapted to be movable, along with the read/write head provided on the read/write head holding means, radially of the disc and having recorded thereon a position information indicative of a moving position of the read/write head and which is readable from outside, the servo signal writing apparatus comprising:
means provided movably in a position corresponding to the moving position of the scale to detect the position information;
means for controlling the read/write head moving means correspondingly to the position informed detected by the position information detecting means to move the read/write head radially of the disc in order to write servo signals to the disc; and
means for moving the position information detecting means correspondingly to a position on the disc where the servo signal is to be written to change the position where the position information is to be detected by the position information detecting means.
In this servo signal writing apparatus, the position where the position information is to be detected is changed by moving the position information detecting means correspondingly to a position on the disc where the servo signal is to be written, thereby writing a servo signal to each of all the recording areas on a disc provided in the disc recording and/or reproducing apparatus.
Also, the above object can be attained by providing a servo signal writing apparatus for writing servo signals to a disc provided in a disc recording and/or reproducing apparatus comprising a read/write head to write and/or read a signal to and/or from a disc; means for holding and moving the read/write head radially of the disc; and a scale adapted to be movable, along with the read/write head provided on the read/write head holding means, radially of the disc and having recorded thereon a position information indicative of a moving position of the read/write head and which is readable from outside, the servo signal writing apparatus comprising:
a plurality of means provided movably in positions corresponding to the moving positions of the scale to detect the position information; and
means for controlling the read/write head moving means correspondingly to the position informed detected by the plurality of position information detecting means to move the read/write head radially of the disc in order to write servo signals to the disc;
the plurality of position information detecting means being used selectively according to the position on the disc where the servo signal is to be written.
In this servo signal writing apparatus, the plurality of position information detecting means is used selectively according to the position on the disc where the servo signal is to be written to detect the position information, thereby writing the servo signal to all the recording areas on the disc in the disc recording and/or reproducing apparatus.